The present invention relates generally to the control of tension variations in a traveling sheet of material, as might occur in a rolling mill or in a leveling apparatus, and particularly to an "exciting means" for directly introducing a variation in the tension of a traveling sheet of material.
Tension in a traveling sheet is a variable that is responsive to changes in processing parameters that cause changes in the quality of the sheet, such as a uniform thickness or gauge and flatness (which is the shape of the sheet across its surface area, including the shape along its length and crosswise of the direction of sheet travel). The sheet itself dynamically connects or couples separate parts of the sheet handling process, such as the individual stands of a multi-stand rolling mill, or between an unwind coil of metal and tension bridles for levelers that remove buckles from the sheet, i.e., variations in sheet tension in one part of a process can confound operations in other parts of the process. For example, tension coupling can contribute to certain types of mill chatter, cyclic process instabilities, and amplification of cyclic variations. Further, variations in sheet tension can effect the deformation processes associated with leveling and rolling operations. By observing the dynamics of the tension process, source causes of tension instability can be identified thereby permitting modifications in equipment and in control processes to eliminate the cause of the problem or at least reduce its effects.
At present there is no means to directly measure the mechanism of dynamic coupling on sheet handling lines. Therefore, it is difficult to assess whether there is significant interaction and amplification of tension variations occurring in a line.